Abstract: To study the detection of the surface-breaking cracks of the ferrite and austenite dissimilar steel welded joint by means of the electromagnetic testing techniques, the transverse and longitudinal notch reference blocks based on Q235R and S30408 dissimilar steel were manufactured, and the eddy current array and the alternating current field measurement techniques were selected to test the blocks. The results show that the eddy current array technique can effectively detect the transverse cracks and the longitudinal cracks at the ferrite and austenite dissimilar steel welded joints, but is unable to detect the longitudinal cracks at the fusion line; whereas the alternating current field measurement is capable of detecting the longitudinal crack at the ferrite and austenite fusion line, but is unable to detect the longitudinal notches at far away from the ferrite area. Therefore, the combination of the eddy current array and the alternating current field measurement techniques may be used to solve the problem on the surface open crack detection of the ferrite and austenite dissimilar steel welded joint.